What is a primary advantage of using a variable frequency drive over a soft starter?

• A. Soft starters provide better speed control than VFDs.
• B. VFDs have no efficiency benefits.
• C. VFDs adjust speed and torque with higher efficiency, while soft starters mainly limit inrush.
• D. VFDs are cheaper and easier to install.

Answer: (C)

A variable frequency drive changes how the motor is fed by adjusting both the frequency and the voltage, so you can set the exact speed and the corresponding torque you need. Because of this, the motor can run at energy-efficient speeds for the actual load, and the drive can smoothly accelerate and decelerate, reducing electrical stress and wear on mechanical components. A soft starter, on the other hand, mainly limits the inrush current at startup by gradually applying voltage; once the motor reaches full speed, it simply runs at full voltage and the fixed line frequency. So the key benefit of a VFD is its ability to control speed and torque with higher efficiency during operation, rather than just limiting startup current.